In view of recent media reports that large capacity power banks can only hold 50 to 60 percent of the capacity label and that the Bureau of Standards, Metrology and Inspection (BSMI) has been neglecting its duty to report these cases, the BSMI provides its explanation here. "Rated capacity" is the maximum amount of power that can be used for discharging, the bureau said. Since power bank lithium batteries have an internal voltage of 3.7V and a standard USB output has 5V, energy will be lost in the transformation between the two voltages. After discounting the loss, only 60 to 70 percent of the energy stored can be discharged for use. The analogy is illustrated in the following picture. 
1)The water level(Lithium battery capacity) is higher because the bottom of the glass(internal voltage) is narrower Lithium battery capacity: 10000 mAh. 2)The transfer of water(discharging) from the small glass to a bigger one will induce a loss in water volume Rated capacity of the power bank: 7400 mAh. 3)The water level(Rated capacity of the power bank) is lower because the bottom of the glass is wider and some water has been lost. 
BSMI Director-General Liou Ming-Jong said that 3C products, including power banks and battery chargers designed for on-the-go charging, have become an indispensable part of life with the advancement of science and technology. In 2013, Consumer Protection Committee under the Executive Yuan randomly tested 20 power banks sold on the market and found out problems such as false labeling of rated capacity. There have also been many reported cases of battery and power bank explosions and burnouts. To protect consumer safety, the BSMI announced that beginning May 1 2014, all secondary lithium battery cells and batteries, secondary lithium mobile power banks and battery chargers for 3C products must pass a mandatory inspection before being marketed in Taiwan. The inspection standard follows CNS 15364, CNS 14336-1 and CNS 13438. As of February 10 2015, the BSMI has issued 1,237 secondary lithium battery and 528 power bank certificates of inspection. The BSMI also conducts annual market surveillance on commodities subject to mandatory inspection and promotes such information on the internet and social networking sites such as Facebook. The bureau has so far finished testing 20 out of the 28 samples purchased in September 2014. Five out of the 20 samples failed to comply with the national standards. A comprehensive result of the inspection will be jointly published by the bureau and the Consumers' Foundation approximately March 2015. BSMI Director-General Liou said that the bureau has already initiated an ad-hoc plan to tighten inspections on power banks sold by internet vendors and retailers in January 2015. It is expected that 210 samples will be inspected by early March. According to Article 50 and Article 60-1 of the Commodity Inspection Act, attempts to place uninspected goods (evasion of inspection) on the market will be fined NT 200,000 to NT 2,000,000. Also, according to Article 6-4 of the same act, sellers shall not display or sell commodities subject to inspection that do not comply with inspection requirements. A second market surveillance, which aims to test the quality of 38 samples that advertise large power capacity, has been launched in February 2015. As of February 10 2015, the bureau has seized 12 items in violation of law. The largest fine imposed so far is NT 250,000, as according to the Administrative Act. Many alleged cases are still under investigation. BSMI Director-General Liou urges importers and suppliers of power banks to provide accurate information to consumers. To avoid confusion, rated capacity should be labeled on the power bank as well as on the outer packaging. Consumers should be aware of the following when selecting and using portable power banks: 1.Preference should be given to power banks products imported or released after May 1 2014 and those that come with a Commodity Inspection Mark. 2.The maximum capacity of the power bank will decrease with time and use. The closer the production date, the better the supply of power. 3."Rated capacity" is the actual capacity output of the power bank. 4.Consumers should avoid purchasing small, cheap power banks with large capacity labels. 5.Consumers should choose power bank capacity and output specifications according to their own needs. 6.Products that come with warranty and insurance are preferred. 7.Store portable power banks in cool, dry places and avoid direct exposure to the sun. Be aware that humid environment can have negative effects on the internal circuit. 8.Avoid putting power banks and inflammable goods or metal products in the same place. 9.Remove lithium batteries from the power source after full charging. Avoid overcharging. Note that over discharging can also reduce battery life. Agency in charge: Mechanical, Electrical and Electronic Inspections Administrative Division (3rd Division) Contact person: Ms. Tzu-Jung, WU Telephone: (02)2343-1763